The objective of this research is to investigate the mechanism of mutagenesis induced by the nitrated pyrenes which are known environmental pollutants and are suspected to pose threats to human health. To accomplish this goal, we propose to use the tools of organic synthesis and recombinant DNA technology to generate specific DNA fragments and viral genomes that contain, at preselected sites, the known DNA adducts formed by these compounds. Physico-chemical studies will be carried out on these modified oligonucleotides to understand the architectural effect of the DNA-bound forms of the nitropyrene metabolites. In separate sets of studies, the modified genomes will be introduced in cells, where the DNA replication and repair systems will act upon the single DNA adduct. Progeny DNA molecules will be isolated, and the mutagenic as well as toxic effect of the single adduct will be studied both qualitatively and quantitatively. Finally, replication of the genome in hosts with defined defects in DNA repair will be carried out. The primary goal of this work is to define the relationship between the structure and three-dimensional effects of a lesion in DNA and the mutagenicity and cytotoxicity that it may cause. Another important aim is to establish which cellular genes protect cells against the mutagenic or toxic properties of this DNA damaging agent.